Modern electronic devices often include components which are bonded and packaged together for purposes such as heat dissipation, electrical grounding, or the like. For example, a circuit board can be bonded to a metal heat sink in order to dissipate heat associated with an operation of the circuit board. Conventional bonding techniques, for example, comprise utilizing a thermal-set adhesive, wherein the circuit board is bonded to the heat sink by an application of heat to the entire electronic device, therein curing the thermal-set adhesive at a substantially high temperature. Such high-temperature curing, however, can have deleterious effects on a planarity of the circuit board once the device is cooled.
For example, FIGS. 1A and 1B illustrate an exemplary conventional electronic device 10 in various stages of fabrication. The electronic device 10 comprises a circuit board 15 and a metal heat sink 20, wherein an adhesive layer 25 resides therebetween. Typically, the circuit board 15 and heat sink 20 have differing coefficients of thermal expansion, wherein the circuit board typically expands and contracts significantly less than the heat sink upon a respective application and removal of heat to the device 10. In FIG. 1A, the circuit board 15 and heat sink 20 are illustrated prior to heating, wherein the adhesive layer 25 is generally un-cured, thus allowing a movement between the circuit board and the heat sink. In the un-cured state, the circuit board 15 and heat sink 20 are generally planar and parallel to one another. In order to cure the adhesive layer 25, the device 10 is heated, and the exemplary circuit board 15 and heat sink 20 generally expand at differing rates. However, since the adhesive layer 25 generally remains in a pliable state below a predetermined cure temperature, the circuit board 15 and heat sink 20 are generally permitted to expand with respect to one another, thus maintaining the planarity when the adhesive is still un-cured.
Once the adhesive layer 25 cures at the predetermined cure temperature, however, the circuit board 15 and heat sink 20 are generally fixed with respect to one another by the cured adhesive. Thus, during a cooling of the device 10, the circuit board 15 and heat sink 20 contract (again, since the circuit board and heat sink have differing coefficients of thermal expansion), generally causing a build-up of stress between the circuit board and heat sink. FIG. 1B illustrates a result of the stress build up, wherein the heat sink 20 generally warps with respect to the circuit board 15 due to the stresses imposed between the heat sink and circuit board. Depending on the elasticity of the adhesive layer 25 and the stiffness of the circuit board 15 and the heat sink 20, for example, an amount of warpage 30 can result, thus leaving the device generally non-planar. Alternatively, the bond between the circuit board 15 and the heat sink 20 by the adhesive layer 25 can succumb to the stresses, thus delaminating the device.
Accordingly, there is a need for improved packaging by which the shortcomings of traditional packaging can be mitigated.